1. Field of the Invention
The invention relates to a method of inserting a background signal into parts of a foreground signal, which parts are fixed by a predetermined key color, in which method a control signal is derived from the foreground signal, which control signal assumes a first value when the foreground signal represents a color in the region of the key color and a second value when the foreground signal represents a different color, in which the control signal has a transition range between the two values, and in which a difference, influenced by the control signal, between the vector of the background signal and the vector of a signal representing the key color is vectorially added to the foreground signal.
2. Description of the Related Art
U.S. patent application Ser. No. P 41 43 180.4, corresponding to the above-noted U.S. parent application, discloses such a method and an arrangement for performing this method. This main Patent relates to a method of inserting a background signal into parts of a foreground signal, in which method a vector, influenced by the control signal, of the difference between the background signal and a predetermined key color is added to the foreground signal. In the most general formulation of the teachings of the main Patent no detailed explanation of the structure of the background signal, of the signal representing the key color and of the foreground signal is given, because the teachings of the main Patent are independent of the special implementation of these signals. In a special implementation of the teachings of the main Patent, given components of these signals are preferably to be processed in accordance with the teachings of the main Patent. In accordance with the teachings of the main Patent, particularly only the chrominance signals are processed, whereas another method is chosen for processing the luminance signals, in which method the luminance component is not extracted subtractively but is rather complementarily faded. Smooth transitions between the picture parts given by the foreground signal and the background signal can then be obtained and particularly the blue fringes can be effectively reduced. Fading of the luminance signals with the complement of the control signal derived from the chrominance components supersedes the additional determination of a separate control signal from the luminance components for the purpose of fading these components.